Noisy Guns

"Clicker-Clack Effect: The firearm counterpart to the Snicker-Snack Effect. Whenever a character is holding a gun and waves it for emphasis, regardless of whether the character actually cocks the gun, or if the gun even has a hammer to cock, it makes a cocking noise."

—Matt Griffin, Ebert's Little Movie Glossary

In real life, guns are carefully designed, well-constructed tools that - provided they are well maintained - can last a lifetime. On TV, they're apparently filled with rusty nails and loose change, and held together with masking tape.

As a result, whenever someone hefts a weapon - particularly if it's a machine gun or submachine gun - it will make a whole load of clicking, clacking and clonking even though all they're doing is rotating it through 90 degrees. This trope is likely the result of the fact that a noisy gun adds drama to the scene. (See: Dramatic Gun Cock and Click. "Hello.")

Media also routinely depicts guns being dry fired more than once when they run out of ammo. The "Click Click Click" sound lets the audience know it's empty. Unfortunately, not all guns in the real world can do this. Pump-action shotguns; single fire rifles; bolt-action rifles; lever-action carbines; and even single-action revolvers, none of these will repeatedly dry fire without a re-cock.

Double action pistols and revolvers will fire on every trigger pull, of course. The name refers to the "double action" of the trigger—every pull advances the cylinder, cocks the hammer, and fires the weapon. You can dry fire a double action weapon all day without ever touching the hammer (of course, you still can't get the empty click-click-click even from a double-action semi-automatic, since the slide will (on the vast majority of designs) lock back on an empty magazine - but that's neither here nor there).

Electrically powered firearms, like the "gatling" cannon used on aircraft, will dry fire as long as you hold down the trigger.

May or may not be a side effect of Shur Fine Guns. Related to Bang Bang BANG. Subtrope of Kinetic Clicking. If you're thinking of intentionally making a noise to announce an entrance or punctuate a phrase, see Dramatic Gun Cock, and please don't add examples of it here. For the Sword Counterpart of this, see Audible Sharpness.

Examples of Noisy Guns include:

Anime

The first episode of Hellsing has this wonderful (but noisy) montage of Alucard putting his gun together before the first scene. Complete with the ramping up of the volume of every little sound such parts would make for maximum effect.
Liberally applied in Monster despite its heavy level of realism.
Trigun also has plenty of rattling guns
Ghost in the Shell is guilty of this. Made worse by the fact that it's the future and said guns are, as you'd imagine, relatively futuristic.
Gundam Wing is also a major offender, punctuating every draw, particularly by Heero, with a bunch of clicking.
In Rurouni Kenshin, the sword variant of this occurs every now and again. Whenever characters slowly move their swords into position, their stopping is punctuated by the rattling of the blade against the internal parts of the hilt. Makes you wonder how those swords stay in such good condition with all the rough treatment they get...
One Piece commonly exhibits this with guns, possibly justified with them primarily being flintlocks. Zoro's swords however, rattling every time he moves them while they are outside of the scabbard, play this straight.
Magical Girl Lyrical Nanoha uses this trope on magtek weapons, but once the Belkin-Cartridge system comes into play, suddenly *Ka-chunk* or a series of clicks/steam expulsion systems get upgraded... the Anime pretty much codifies this trope among the magical girl genre.

Film

The Matrix has a guard draw a Glock, a polymer-framed striker-fired pistol, which immediately produces a chorus of clicks. Being striker-fired, Glock pistols only make that much noise when you move the slide back to chamber a round, a big motion best done with your other hand. He'd have to do that if he wanted to fire it, but you can't do that just by drawing the gun.
A very obvious example occurs at the end of the recent The Pink Panther starring Steve Martin. A guard tightens his grip on his Glock, and it makes a cocking noise for no apparent reason.
Parodied in Robin Hood: Men in Tights, where a crossbow makes a bunch of clicky-gun-noises like a sniper rifle being assembled.
When it's all gone seriously wrong, near the close of Crimson Tide, two groups of submariners are pointing guns at each other. Every move they make seems to result in their guns being cocked, going by the soundtrack.
Played straight in V for Vendetta with Creedy, although he was using a revolver so it's justified.
Inverted in The Good, the Bad and the Ugly when Tuco is displeased with the loud clicks that a revolver makes as its cylinder is turned, indicating its poor quality. He dismantles several pistols to construct his own from the parts, and then demonstrates to the clerk that the new gun clicks very softly when its cylinder is rotated.

Literature

Parodied in Artemis Fowl, where the faux-macho LEP squad "coaxed whatever metallic sounds they could out of their weapons".

Live Action TV

Not so much a weapon as a tool (even though many of its uses could be weaponised and it has been used as one), but the Doctor's super-advanced alien tech sonic screwdriver frequently rattles like an old butterfly corkscrew. This only ever seems to happen when the screwdriver is on-screen.

Craig: Can't you make that thing be quiet?
The Doctor: No! It's a sonic screwdriver!

- In The End of Time, every time The Doctor switches between aiming at the Master and aiming at Rassilon, he seems to recock the gun.
  - The Doctor Who universe is one where simply pointing a gun at a person cocks it, sometimes multiple times.
Common in Firefly, though the weapons tend to make futuristic-sounding "zip-click" and "powering up" noises when being pointed.
Common in Human Target, for example, about 15 minutes into "Salvage and Reclamation", when essentially everyone in Maria's bar pulls a gun on Chance, with a range of guns all the way from what appears to be an old Colt revolver to an AK represented. Seems to verge into that particular homage/lampshading/AffectionateParody realm the show is known for when they sort of re-emphasized the brandishing of their guns a few moments later and the exact same sounds are heard.
This accompanies almost every episode of Lost. Pistols make mechanical clinking noises whenever they're waved around and a cocking noise whenever pointed at someone. Most annoyingly, shotgun cocking sounds routinely accompany the raising of any bolt action rifle (it's essentially a 'this weapon gesture is threatening!' code for the viewer). Anyone who's ever used a bolt action rifle will find this infuriating.
Happens to Buffy every time she picks up a crossbow pistol, despite there not being anything to 'click'.

Video Games

Team Fortress 2, has every gun (And some non-guns, such as the Spy's knife) make distinct noises when you switch weapons. The noisy knife actually makes sense, since it's a butterfly knife. The guns...not so much.
Unreal Tournament is also a pretty bad offender. With the background music off, it's entirely possible to track an enemy from the noise of switching weapons and picking up ammo.
In Deus Ex, JC's 10mm sidearm apparently has some kind of very loud three-part safety he has to take off when he draws it. Every time.
Metal Gear Solid 2: Sons of Liberty. Every time Raiden lifts his pistol, it sounds like he's cocked it.
- Similar to both this and the Unreal Tournament example above, if you ever play a game of Metal Gear Online, turn the background music off and you can hear everything from the realistic sound of your opponents footsteps and equipment rustling to the unfortunately unrealistic click of his gun being brought to an 'aimed' position. May be justifiable as your character flicking the safety off...and on, and then off and on again, every half second.
Played straight and justified in Mass Effect, where drawing a weapon causes it to click and clack. Justified in that guns in the Mass Effect universe all fold up when not in use and reassemble when a button is pushed (which is obviously done as the gun is drawn).

Web Comics

In the "Ocean's Unmoving" arc of Sluggy Freelance:

"Hey, why doesn't my gun make a 'chakat' sound?"
"You're set on 'Goo', you have to set it to 'Mexican standoff'."

Web Original

Freddie Wong is particularly guilty of this in his short films, but seems to use it for a full 'action film' effect and for Rule of Cool.

Truth in Television

WWII era Thompson Submachine Guns (AKA "Tommy Guns") made a clacking sound when shaken; a major disadvantage in close quarters fire fights. One of the reasons that the iconical round drums were retired, along with fragility, size and reliability, was because they were too noisy to carry around.
Another WW 2 era weapon, the Japanese Type 99 Rifle, was fitted with a bolt cover that would rattle, often giving away the position of troops in the field.
- It was a very common practice for soldiers to remove the dust cover on their rifles.
Back on the US side, the M1 Garand's en bloc clip made a distinctive pinging noise if it hit a hard surface after ejection. This was a generally a bad thing, although some troops used it to their advantage by throwing empty clips on the ground, thus drawing out enemies who could then be shot with a quite operational rifle. This is one of the more famous aspects of the rifle, to the point that films and video games featuring the rifle typically make the sound as loud as the gunshots themselves and tie it to the clip ejecting from the rifle, regardless of what it lands on.
In "Lad's Army", putting teenagers of today through the National Service of New Zealand of the 1950's - one former serviceman recalled that, in order to make their (unloaded) rifles make louder noises while drilling, they would place a coin in the (empty) magazine.
Belt-fed machine guns are another real life example, as the heavy metal belts make quite a bit of clanking.
- The FN Minimi (designated the M249 by the US army) originally used plastic drums that clacked when the belt inside shifted position, such as when the gun was fired or moved.
M1911 pistols of any brand, from low-end RIA M1911s to never-fired Springfield Armory M1911s fresh out of the case, tend to have a bit of a rattle when moved. Considering the M1911's ridiculous popularity in the USA, it's probably the Trope Maker.